The peak rating is only going to be good for very tiny bursts. Typically only a few milliseconds, and I can guarantee that many ebike setups will draw much more than 6A for at least a few seconds at startups from a stop. The diode could probably take a significant overcurrent for a short period if it is heatsinked well enough, but repeatedly doing that frequently may not let it cool enough.
Trying to run more than the 6A continuous max rating will cook it even if it is heatsinked, eventually. How long that eventually is depends. What's ambient temp? What is the heatsink's ability to remove heat? How long does the core of the part stay hot? (one rating I saw was that 6A is only at 75C and lower, so the hotter it gets the less it can handle, too).
You're probably going to want to search for "ideal diode" here on ES using the google site search. Otherwise, you could look for diodes that are packaged in metal bolt-on types. Kind of like this:
http://www.tme.eu/katalog_pics/1/7/5/17 ... -10-10.jpg
Those can be threaded right into a heatsink (or metal mounting plate), and generally are designed for very high currents.
I am not sure, but I think Ping directly sells the 100V 100A diodes (thought I read that somewhere in a similar thread).